1. Technical Field
The present invention relates to an electronic device for detecting interaction between the human body and the invented device permitting noninvasive determination of the glucose concentration in parts of the human body, in particular, in the human blood.
2. State of the Art
1.1 Physical Background
1.1.1 Heat and Temperature
Heat or rather thermal energy is the sum of the individual kinetic energy of the components of the material. This mean energy is the same for all particles, although independent of its mass: EQU &lt;W&gt;=1/2m&lt;v.sup.2 &gt;
Temperature is only another measure for the mean kinetic energy of the molecules. If only the translation energy is considered, its mean value is given by EQU &lt;W.sub.trans &gt;=1/2m&lt;v.sup.2 &gt;=3/2k T.
In this general definition of temperature m stands for the mass, &lt;v.sup.2 &gt; for the square average velocity of the molecules. The Boltzmann constant k has the value of EQU k=1.381.times.10.sup.-23 J K.sup.-1.
1.1.2 Temperature Measurement
Fundamentally, a temperature measurement procedure can be based on every known reproducible relationship between a material property and the temperature. In practice, e.g., the expansion of fluids, the change in electric resistors, the change in the sonic velocity in solid bodies, etc. are drawn upon for the measurement of temperature.
1.1.2.1 Thermistors and Thermo-elements
Certain thermistors and thermo-elements are particularly suited, due to their small mechanical dimensions, for temperature measurement within the scope of the present invention.
In most semiconductors, the temperature coefficient of the electric resistance is negative (high-temperature conductor, or "NTC-resistor" or called in short "NTC" &lt;negative temperature coefficient&gt;).
Thermo-elements are the electric thermometers most frequently employed in the temperature range of 1 K to 3000 K. Although the measurement uncertainty is larger than that of the resistors, the thermo-elements are much easier to produce, have small spatial dimensions, possess a short response period and are especially suited for measuring temperature differences. Voltage compensators or high-ohmic voltmeters are employed for measuring the thermo-electric voltage.
1.1.3 Mechanism of Heat Transport
Thermal energy can fundamentally be transported either by radiation, heat conduction or flow (convection).
1.1.3.1 Heat Radiation
Heat radiation is of an electro-magnetical nature such as light. It permits releasing heat even into a vacuum. This release is only dependent on the temperature of the radiating body. Heat radiation is also called temperature radiation or thermal radiation.
1.1.3.2 Heat Flow
Heat flow presupposes macroscopic movements in fluids or gases, the heat content of which is transported in this manner to other sites.
1.1.3.3 Heat Conduction
Heat conduction occurs only in material but is however not connected to its macroscopic movement, but rather to the energy transfer due to the impact between the molecules. It presupposes local differences in the molecular energy, that is, drops in temperature. Frequently, it is the heat transport which sets off this temperature drop that generally results in temporal change of the temperature distribution.
1.1.3.3.1 Heat Conduction in Insulators
In metals, heat like the electric current is transported predominantly via conduction electrons, in the insulators however, heat is transported via phonons. Phonons are respectively quanta (smallest amounts of energy) of elastic lattice vibrations of the wavefield generated therefrom. Just as the heat content of a solid body can be considered the energy of its phonon gas, heat conduction therein occurs as the transport phenomenon in the phonon gas. Thermal energy can be transported in a gas in two ways:
a) as supplementary energy of a flowing gas which is hotter than its surroundings like in a heat exchanger, or PA1 b) as energy diffusion in a resting gas while maintaining a temperature gradient, with the gas being in a thermal equilibrium with its surroundings at every site.
Only the second procedure (b) is heat conduction. The heat conductivity is the proportional constant between heat flow and T-gradient.
1.2 Physiological Background
1.2.1 Biological Rhythms of Blood Glucose
Close-mesh blood glucose day and night profiles of normal individuals and ill individuals show similarities such as a rise in the evening, a drop during the night, another rise in the early morning. This is true despite very different external factors such as age, nutrition, illness, etc. These similarities seem to reflect endogenic and vegetative periodicity. Such periodic fluctuations are called circadian rhythms. This refers to biological rhythms with a period length of about 24 hours. This biological rhythm continues even if two important environmental periodicities such as light and ambient temperature are maintained constant.
In a multicell organism, the functions of the entire organism as well as that of the individual organs and cells are subject to rhythms which are in a specific relationship to one another and to the periodicity of the environment and are called "circadian organization". Glycogens, glycogen synthase and glycogen phosphorylase and the corresponding blood glucose concentrations permit detecting a distinct, parallel rhythm.
In humans, the vegative functions such as pulse, blood pressure, respiration, body temperature, etc. also are subject to circadian periodicity. Activity phases, e.g., have durations with individual fluctuations lasting from 0800-1200 and 1600-1900 hours. During this time, metabolism is catabolic. Raised are, e.g., the body temperature, the blood pressure and the blood glucose concentration. During this time, the person is able to work. In contrast, the vagotonic recovery phases are between 1300-1500 and 2200-0600 hours. During these phases, the aforementioned parameters are low and the person is ready to sleep. These phases are subject to time shifts which can be schematically allocated to a morning person or a night person.
1.2.2 Physiology and Regulation of the Body Temperature
The predominant chemical heat producing processes and physical heat loss processes are related in a control circulatory system.
The heat loss processes (physical thermal regulation) were divided into heat conduction, heat radiation, heat flow, evaporation, respiration and secretion. Belonging to the heat producing processes are 1) minimal heat production due to a) essential energy production and b) obligatory heat production; 2) nutrition-inducible heat production; and 3) regulatory heat production with a) increased muscle activity and b) without muscle activity.
As the body always tries to maintain a constant core temperature with changing ambient temperature, the heat production and heat absorption has to be brought into equilibrium with the heat loss.
In order to be able to determine a temperature on the surface of the skin, it is first important to ascertain the amount of heat which passes through the surface of the skin. The greatest part of the heat is dissipated to the surroundings via the skin. The four essential types of heat transfer will be briefly described again.
Heat conduction refers to heat exchange between adjacent site-fixed particles.
Heat convection describes the heat transport of moving particles (blood, air). Heat radiation characterizes every electro-magnetic radiation, in this case temperature radiation without any relay of a material heat carrier. The evaporation, on the other hand, is a measure of the heat transport during the transition from the fluid phase to the gaseous phase.
At room temperature and rest conditions, the greatest part of the heat amounts are released by radiation. The rise in heat production following a meal is caused by nutrition-inducible thermogenesis. This can be explained by ATP loss resulting from the conversion of the ingested nutrients into body-own substances. The influence of humidity on heat regulation has to be taken into account.
Heat flow from the interior to the exterior is composed of two parts. The first part describes the transition core-skin, the second the transition skin-surroundings.
The thickness and thermal conductivity of the media through which the heat is transported as well as the heat transition conditions influence the heat transport. The skin temperature is therefore a function of the interior and exterior heat transport and transition conditions.
Conductive heat transport is only encountered in the top layers of the epidermis. Convective transport with blood predominates in the entire remaining organism. The extremities take on a special position. The heat resistance, between the core and the surface can be set maximally large or minimally small. They act according to the principle of a countercurrent heat exchanger.
The following discusses skin temperature and skin blood circulation. In the zone of metabolic neutrality, the core temperature is regulated by controlling heat loss. The skin temperature changes more steeply here than in other areas.
Below 20.degree. C., blood circulation is minimal and therefore the temperature drop skin-room and heat loss are zero. If the room temperature rises, the increase in blood circulation leads to a rise in skin temperature.
Under constant conditions, core and surface temperature are subject to fluctuations in daily rhythm. The values of the extremities drop by about 4-5.degree. from 0600 am to 1200 noon. However, they then stay at this level. In the evening, the temperature of the extremities rises again. On the other hand, the core temperature rises again until 1800 o'clock and then drops again. The surface temperatures at the head and throat follow the course of the core temperature. Fluctuations in temperature are based on changes in the blood circulation in the skin. The blood circulation in the feet, e.g., in the afternoon is less than at night. Blood circulation on the forehead runs parallel to the core temperature.